This week we worked with composites. I worked with my colleagues here in the Detroit Fab Lab to design and model a mold, then use it to mold a composite object. We decided to make a holding tray and what I thought would be a couple days of project turned out to be a very long week. I designed the mold using Sketchup.

Once we had the design drawn, I went back to make a correction to taper the sides of the mold, both the male and female parts, to make it easier to lift out once it was done. I helped to nail down a surface and then taped the foam model down as we began to cut it on the shop bot. The model was cut from foam so it was not the easiest thing to machine on the shop bot. In fact, we had to glue three layers together to get the right thickness and depth. We had to make trips to the hardware store to get adhesive for this, as well as paste wax to keep the composite from sticking to the foam.

After the male mold was cut satisfactorily, I applied a layer of gesso and paste wax. Next we sanded it down and I heated it with a hot air gun to dry the gesso quickly and seal open areas of the mold.

After this, we cut pieces of paper in the shape of the surface of the mold to make sure out fabric would fit the way we liked. I drew the fabric design to angle over all of the surfaces and sides of the mold so that we would have complete coverage. We still descided to use additional strips of fabric to cover the corners because they looked as though they would be structurally weak. We only added three layers of strips so that the composite wouldn't be extra thick in the corners

Next we went through a test run before we actually began laying-up the composite materials and epoxy. Others in the lab had already gone through this process and we were able to watch them before we went through the process. This is something I would recommend for others because once the epoxy is out and mixed it will definitely start to get hot and harden and your 15-20 minutes of potlife will go fast. Doing a dry run or watching others first will help you visualize the entire process and make fewer mistakes while the clock is ticking. All three of us had to work to apply the epoxy quickly and stretch the fabric over the mold. We then placed a layer of release film and breather material over both sides. WEST SYSTEM, the company which sells the epoxy mold we used, makes a vacuum baggin tutorial available on their website. It is a good source for beginner vacuum baggers as well as a useful guide for learning about vacuum bagging techniques and troubleshooting resources as well. We seemed to move frantically as we went through the vacuum bagging and lay-up process, even with three people working. I would say that having someone there is helpful for handling all of the various parts and materials that you have to use in this process and the bigger the project the more likely you are to need assistance in certain parts of the process like bagging. When going through this alone, it cannot be overstated that preparation and planning are critically important to making sure this process goes safely and smoothly.

After it was vacuumed sealed for and hour and a half, we removed the mold from the bag. The only problem we had at this step was that the paste wax had been applied in a thin layer and peeled off the surface of the foam mold. This taught me that gesso and wax can make it easier to release a foam mold used in vacuum bagging but that the gesso must cover the piece entirely and the wax should be applied generously to coat the surfaces and prevent the peeling we had. It made the surface of the tray look blotchy. the outside bottom of the tray turned out to be better looking than the inside for this reason. Also, one should not underestimate the stickyness of the resin on the materials used in the vacuum baggin process. We had a area where some of the composite material pinched the release film and it was hard to get out. Giving the bag enough room to pull tight helps create a seamless surface helps. Adding breather material in several layers under the suction cup helps prevent distortion on the surface of the composite.

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